The combination of electronic engine management systems and other emission controls has eliminated anywhere from 90-99% of noxious pollutants from modern cars. The problem is that these systems rely on an array of sensors to manage the fuel/air mixture, and when they fail emissions skyrocket. For several decades drivers, in California have had to get regular emissions checks before renewing their registration. Now drivers won't have to wait until their annual checkup, as the South Coast Air Quality Management District has a mobile emissions check van that evaluates cars remotely as they drive by.
The infrared and ultraviolet sensor equipped van parks on on-ramps and takes a picture of polluting cars as they pass by. A letter is sent to the car owner suggesting the car either be repaired or scrapped. There is also a volunteer program that will provide $500 toward repairs or $1,000 to scrap the car. Since the program started in March, 2,000 letters have been sent out. With 10% of vehicles producing over half of the pollution, the program is intended to catch people who are either cheating or making temporary repairs just to pass the annual test and get those vehicles off the road.
[Source: LA Times]